Wafer-level optoelectronic packaging

ABSTRACT

A wafer-level optoelectronic packaging method includes fabricating a pre-singulated wafer. The pre-singulated wafer has a plurality of sub-mounts. A first sub-mount of the plurality of sub-mounts includes an optical waveguide formed on a substrate, a multi-layered sub-mount boundary wall that is formed on the optical waveguide, and a v-groove that is external to the sub-mount boundary wall. A plurality of optical dies are attached to the corresponding plurality of sub-mounts, such that each optical die is aligned to the optical waveguide of the corresponding sub-mount. A cap-wafer including a plurality of caps is attached to the pre-singulated wafer to obtain an encapsulated pre-singulated wafer. The encapsulated pre-singulated wafer is diced to obtain a plurality of optoelectronic packages. The optical waveguide of each optoelectronic package serves as an interconnection conduit between the corresponding optical die and an optical fiber placed in the corresponding v-groove.

The present patent application is continuation and claims priority fromU.S. Utility application Ser. No. 16/860,615, filed on Apr. 28, 2020,which continuation and claims priority from U.S. Utility applicationSer. No. 15/802,009, filed on Nov. 2, 2017, which are hereinincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to optoelectronic communication systems,and more particularly to a method for manufacturing optoelectronicpackages for optical coupling.

BACKGROUND

Optoelectronic packages generally include one or more optical dies, suchas waveguide-based diode lasers, photo-detectors, and planar lightwavecircuits (PLCs), enclosed in a cavity formed by a cap and a substrate towhich the optical dies are attached. Optical signals from the opticaldies are coupled to an optical fiber for communication over longdistances. The optoelectronic packages generally rely on free spacelight propagation for transmitting the optical signals from the cavityfor coupling with the optical fiber or an optical waveguide.

FIG. 1 shows a cross-sectional view of a first conventionaloptoelectronic package 100 for coupling optical signals to an opticalfiber 102. In the first conventional optoelectronic package 100, anoptical die 104 is attached to a sub-mount substrate 106, and a mirror108 is fitted in a mirror guiding hole (not shown) formed on thesub-mount substrate 106. A cap 110, having a cavity 112, is attached tothe sub-mount substrate 106 by way of a bond layer 114 therebetween. Thebond layer 114 can be made from various materials, such as adhesiveresins, solder material, and the like. The cap 110 includes a first lens116 fitted in a lens guiding hole (not shown) that is formed on the cap110. The mirror 108 receives a first optical signal OS1 that is parallelto the surface of the sub-mount substrate 106 from the optical die 104.The mirror 108 reflects the first optical signal OS1, thereby making thefirst optical signal OS1 perpendicular to the surface of the sub-mountsubstrate 106. After reflection, the first optical signal OS1 propagatesin free space through the cavity 112 and the cap 110, and becomesincident upon the first lens 116. The first lens 116 focusses the firstoptical signal OS1 onto a second lens 118. The second lens 118 couplesthe first optical signal OS1 to the optical fiber 102, which in turntransmits the first optical signal OS1 over long distances to one ormore remote devices (not shown).

FIG. 2 shows a cross-sectional view of a second conventionaloptoelectronic package 200 for coupling optical signals to an opticalwaveguide 202 of a silicon photonic chip 204. In the second conventionaloptoelectronic package 200, an optical die 206 is attached to asub-mount substrate 208. A cap 210, having a cavity 212, is attached tothe sub-mount substrate 208 by way of a bond layer 214 therebetween. Thebond layer 214 can be made from various materials, such as adhesiveresins, solder material, and the like. The optical die 206 emits asecond optical signal OS2 in a direction that is parallel to the surfaceof the sub-mount substrate 208. The second optical signal OS2 becomesincident upon the internal surface of the cap 210, which is coated witha reflective material. The internal surface of the cap 210 reflects thesecond optical signal OS2. After reflection, the second optical signalOS2 propagates in free space through the sub-mount substrate 208, andbecomes incident upon a third lens 216. The third lens 216 focusses thesecond optical signal OS2 onto a grating coupler 218, which is mountedon the optical waveguide 202. The grating coupler 218 couples the secondoptical signal OS2 to the optical waveguide 202, which in turn maycouple the second optical signal OS2 to an optical fiber (not shown) fortransmission to one or more remote devices.

In the first and second conventional optoelectronic packages 100 and200, the first and second optical signals OS1 and OS2 undergo highpropagation and reflection losses due to propagation in the free space,respectively. Further, the poor coupling efficiency of the second andthird lenses 118 and 216 results in coupling losses of the first andsecond optical signals OS1 and OS2 into the optical fiber 102 and thegrating coupler 218, respectively. A known solution for improving thecoupling efficiency of the second and third lenses 118 and 216 is to useactive alignment techniques for aligning the optical path of the secondand third lenses 118 and 216 to the optical path of the optical fiber102 and the grating coupler 218, respectively. However, the activealignment techniques are complex to implement. Further, the gratingcoupler 218 can couple optical signals that lie in a particularwavelength range to the optical waveguide 202. Thus, the grating coupler218 limits the operational wavelength bandwidth of the secondconventional optoelectronic package 200, which is undesirable.

In light of the foregoing, there exists a need for an optoelectronicpackage that prevents the propagation of optical signals in free space,has less propagation and reflection losses, large operation wavelengthbandwidth as compared to the first and second conventionaloptoelectronic packages 100 and 200, and does not require additionalcomponents, such as lenses, for coupling the optical signals at itsoutput.

SUMMARY

In an embodiment of the present invention, an optoelectronic package isprovided. The optoelectronic package includes a sub-mount, an opticaldie, and a cap. The sub-mount includes an optical waveguide that isformed on a substrate, and a sub-mount boundary wall that is formed onthe optical waveguide. The sub-mount boundary wall includes a firstdielectric layer formed on the optical waveguide, and a first metallayer formed on the first dielectric layer. The sub-mount boundary wallfurther includes a second dielectric layer formed on the first metallayer, and a second metal layer formed on the second dielectric layer.The optical die is attached to the sub-mount. The cap is attached to thesub-mount to form a cavity for enclosing the optical die.

In another embodiment of the present invention, a method for wafer-leveloptoelectronic packaging is provided. The method includes fabricating apre-singulated wafer having a plurality of sub-mounts that include afirst sub-mount. The first sub-mount includes an optical waveguideformed on a substrate, and a sub-mount boundary wall that is formed onthe optical waveguide. The sub-mount boundary wall includes a firstdielectric layer formed on the optical waveguide, and a first metallayer formed on the first dielectric layer. The sub-mount boundary wallfurther includes a second dielectric layer formed on the first metallayer, and a second metal layer formed on the second dielectric layer. Afirst optical die of a plurality of optical dies is attached to thefirst sub-mount. A cap-wafer including a plurality of caps is attachedto the pre-singulated wafer for obtaining an encapsulated pre-singulatedwafer, when each of the plurality of optical dies is attached to thecorresponding sub-mount. The encapsulated pre-singulated wafer is dicedto obtain a plurality of optoelectronic packages. A first optoelectronicpackage of the plurality of optoelectronic packages includes the firstoptical die enclosed within the cavity formed by a first cap of theplurality of caps and the first sub-mount.

In yet another embodiment of the present invention, a plurality ofoptoelectronic packages manufactured by the method as described in theforegoing is provided.

Various embodiments of the present invention provide a method foroptoelectronic packaging at wafer-level and an optoelectronic packagemanufactured by performing the method. A pre-singulated wafer isfabricated by performing one or more wafer processing operations, suchas patterned deposition, etching, lithography, and the like, on a firstsubstrate. The pre-singulated wafer has a plurality of sub-mounts thatinclude a first sub-mount. The first sub-mount includes an opticalwaveguide formed on the first substrate, and a sub-mount boundary wallformed on the optical waveguide. A v-groove is formed on the firstsubstrate for each of the plurality of sub-mounts by etching the firstsubstrate. The v-groove of each sub-mount is external to thecorresponding sub-mount boundary wall. The sub-mount boundary wall is amulti-layered structure that includes a first dielectric layer formed onthe optical waveguide, a first metal layer formed on the firstdielectric layer, a second dielectric layer formed on the first metallayer, and a second metal layer formed on the second dielectric layer.The first metal layer is a high-frequency electrical wiring trace andthe second metal layer is a solder layer. The pre-singulated wafer hasuniform topography height, such that the sub-mount boundary walls of theplurality of sub-mounts have same height.

A first optical die of a plurality of optical dies is permanentlyattached to the first sub-mount by way of soldering. The opticalwaveguide is aligned with the first optical die for receiving an opticalsignal from the first optical die. A cap wafer is fabricated byperforming one or more wafer processing operations, such as deposition,etching, lithography, and the like, on a second substrate. The cap waferhas a plurality of caps including a first cap. The first cap has firstand second openings. When the plurality of optical dies are permanentlyattached to the corresponding sub-mounts, the cap wafer is attached tothe pre-singulated wafer for obtaining an encapsulated pre-singulatedwafer by way of hermetic sealing. When the cap wafer is attached to thepre-singulated wafer, the first cap overlaps the first sub-mount to forma cavity for enclosing the first optical die. The cavity is ahermetically sealed cavity. The first opening of the first cap exposesthe v-groove of the first sub-mount, and the second opening exposes thefirst metal layer that lies outside the cavity.

The encapsulated pre-singulated wafer is then diced to obtain aplurality of optoelectronic packages including a first optoelectronicpackage. The first optoelectronic package includes the first optical dieenclosed within the cavity formed by the first cap and the firstsub-mount, and the v-groove of the first sub-mount. An optical fiber isplaced in the v-groove of the first optoelectronic package. When theoptical fiber is placed in the v-groove, the optical fiber gets alignedwith the optical waveguide that lies outside the cavity for receivingthe optical signal from the first optical die.

In the first optoelectronic package, manufactured by the method asexplained in the foregoing, the optical waveguide is accurately alignedwith the first optical die for receiving optical signals from the firstoptical die and is further aligned with the optical fiber for couplingthe optical signals to the optical fiber, with high coupling efficiency.Thus, the optical waveguide serves as an interconnection conduit betweenthe first optical die and the optical fiber for propagation of theoptical signals emitted by the first optical die. Hence, the firstoptoelectronic package prevents the propagation of the optical signalsin free space, and hence reduces the propagation losses. The opticalwaveguide further eliminates the need of additional components, such aslenses and grating couplers for coupling the optical signals from thefirst optical die to the optical fiber. The first optoelectronic packagehas large operational wavelength bandwidth as it does not use thegrating coupler.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of systems,methods, and other aspects of the invention. It will be apparent to aperson skilled in the art that the illustrated element boundaries (e.g.,boxes, groups of boxes, or other shapes) in the figures represent oneexample of the boundaries. In some examples, one element may be designedas multiple elements, or multiple elements may be designed as oneelement. In some examples, an element shown as an internal component ofone element may be implemented as an external component in another, andvice versa.

Various embodiments of the present invention are illustrated by way ofexample, and not limited by the appended figures, in which likereferences indicate similar elements, and in which:

FIG. 1 shows a cross-sectional view of a first conventionaloptoelectronic package for coupling optical signals to an optical fiber;

FIG. 2 shows a cross-sectional view of a second conventionaloptoelectronic package for coupling optical signals to an opticalwaveguide of a silicon photonic chip;

FIG. 3 is a top view illustrating a pre-singulated wafer, in accordancewith an embodiment of the present invention;

FIGS. 4A-4F illustrate steps for fabricating a first sub-mount of theplurality of sub-mounts of FIG. 3 , in accordance with an embodiment ofthe present invention;

FIGS. 5A and 5B illustrate steps for fabricating a cap-wafer, inaccordance with an embodiment of the present invention;

FIG. 6 is a cross-sectional view of a first cap of the cap-wafer ofFIGS. 5A and 5B, in accordance with an embodiment of the presentinvention;

FIGS. 7A-7C are cross-sectional views that illustrate a wafer-leveloptoelectronic packaging method, in accordance with an embodiment of thepresent invention;

FIGS. 8A-8C are top views that illustrate a wafer-level optoelectronicpackaging method, in accordance with an embodiment of the presentinvention; and

FIG. 9 is a flow chart that illustrates the wafer-level optoelectronicpackaging method of FIGS. 7A-7C and FIGS. 8A-8C, in accordance with anembodiment of the present invention.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description of exemplary embodiments isintended for illustration purposes only and is, therefore, not intendedto necessarily limit the scope of the present invention.

DETAILED DESCRIPTION

The present invention is best understood with reference to the detailedfigures and description set forth herein. Various embodiments arediscussed below with reference to the figures. However, those skilled inthe art will readily appreciate that the detailed descriptions givenherein with respect to the figures are simply for explanatory purposesas the methods and systems may extend beyond the described embodiments.In one example, the teachings presented and the needs of a particularapplication may yield multiple alternate and suitable approaches toimplement the functionality of any detail described herein. Therefore,any approach may extend beyond the particular implementation choices inthe following embodiments that are described and shown.

A “substrate” as used herein and throughout this disclosure refers to,but is not limited to, a surface upon which semiconductor structures,such as a single-mode dielectric optical waveguide (SMDOW) andembodiments of the invention may be formed. This may include, but not belimited to, InP, GaAs, silicon, silica-on-silicon, silica,silica-on-polymer, glass, a metal, a ceramic, a polymer, or acombination thereof.

A “metal” as used herein and throughout this disclosure refers to, butis not limited to, a material (element, compound, and alloy) that hasgood electrical and thermal conductivity as a result of readily losingouter shell electrons. This may include, but not be limited to, gold,chromium, aluminum, silver, platinum, nickel, copper, rhodium,palladium, tungsten, and combinations of such materials.

References to “an embodiment”, “another embodiment”, “yet anotherembodiment”, “one example”, “another example”, “yet another example”,“for example” and so on, indicate that the embodiment(s) or example(s)so described may include a particular feature, structure,characteristic, property, element, or limitation, but that not everyembodiment or example necessarily includes that particular feature,structure, characteristic, property, element or limitation. Furthermore,repeated use of the phrase “in an embodiment” does not necessarily referto the same embodiment.

Referring now to FIG. 3 , a top-view illustrating a pre-singulated wafer300, in accordance with an embodiment of the present invention, isshown. The pre-singulated wafer 300 includes multiple sub-mounts ofwhich first through fourth sub-mounts 302A-302D are shown. The secondthrough fourth sub-mounts 302B-302D are structurally and functionallysimilar to the first sub-mount 302A. The top view of the pre-singulatedwafer 300 further illustrates first and second singulation axis 304A and304B of the pre-singulated wafer 300. The first and second singulationaxis 304A and 304B represent the axis along which the pre-singulatedwafer 300 may be diced.

The top view of the first sub-mount 302A illustrates a first substrate306, an optical waveguide 308, first and second dielectric layers310-312, first through third metal layers 314-318, and a v-groove 320.The pre-singulated wafer 300 may be used to manufacture a plurality ofoptoelectronic packages.

The fabrication of the first sub-mount 302A is explained in conjunctionwith FIGS. 4A-4F. The fabrication of the second through fourthsub-mounts 302B-302D is similar to the fabrication of the firstsub-mount 302A. Further, the second through fourth sub-mounts 302B-302Dare fabricated simultaneously with the first sub-mount 302A.

Referring now to FIGS. 4A-4F, steps for fabricating the first sub-mount302A, in accordance with an embodiment of the present invention, areshown. The steps for fabricating the first sub-mount 302A are explainedwith reference to the section A-A′ of the pre-singulated wafer 300.

The structure 400A illustrates the first substrate 306 on which theoptical waveguide 308 is formed. The first substrate 306 may be formedfrom various materials. Examples of such materials include semiconductormaterials; such as silicon, ceramic materials; such as aluminum nitride,and amorphous materials; such as glass, quartz, and the like. Theoptical waveguide 308 is formed on the first substrate 306 by using athin-film dielectric deposition method. The optical waveguide 308includes a lower cladding layer 308A, a core layer 308B, and an uppercladding layer 308C. The optical waveguide 308 is a single-modedielectric optical waveguide (SMDOW) that allows a single-mode opticalsignal having only a fundamental transverse electronic mode, i.e.,TEM(00), to propagate through it. A refractive index of the core layer308B is greater than refractive indices of the lower and upper claddinglayers 308A and 308C. The optical waveguide 308 may be formed fromvarious materials; such as dielectric materials that include silica,silicon nitride, ceramic materials; such as aluminum nitride, andamorphous materials; such as glass, quartz, and the like.

The optical waveguide 308 is etched by using a first patterned mask (notshown) to obtain the structure 400B. Due to etching of the opticalwaveguide 308, the first substrate 306 is exposed in opening portions402A-402C.

With reference to FIG. 4B, the first dielectric layer 310 is depositedin the opening portions 402A-402C and on the optical waveguide 308 ofthe structure 400B to obtain the structure 400C. The first dielectriclayer 310 is a thin-film dielectric material. Examples of the materialsused for forming the first dielectric layer 310 may include aphotosensitive polyimide dielectric material.

The first dielectric layer 310 is then patterned by using a secondpatterned mask (not shown). In an embodiment, a photolithographytechnique may be used for patterning the first dielectric layer 310. Inthe photolithography technique, the first dielectric layer 310 may beexposed to light by way of the second patterned mask. Due to patterningof the first dielectric layer 310, the first substrate 306 is exposed inopening portions 402D and 402E, and the optical waveguide 308 is exposedin opening portions 402F and 402G to obtain the structure 400D.

With reference to FIG. 4C, the first metal layer 314 is then depositedon the first dielectric layer 310. The first metal layer 314 is ahigh-frequency electrical wiring trace that supports high-performanceelectrical connectivity within a range of 0 Hz to 40 GHz. Examples ofmaterials used for forming the first metal layer 314 may include gold,chromium, aluminum, silver, platinum, nickel, copper, rhodium,palladium, tungsten, and combinations of such materials. The first metallayer 314 may be formed on the first dielectric layer 310 by usingpattern deposition techniques. The first dielectric layer 310 isolatesthe first metal layer 314 from the first substrate 306 and the opticalwaveguide 308 to prevent any electrical contact. Due to the depositionof the first metal layer 314 on the first dielectric layer 310, thefirst dielectric layer 310 is exposed in opening portions 402H and 4021to obtain the structure 400E.

The second dielectric layer 312 is then deposited on the first metallayer 314, the first dielectric layer 310 that is exposed in the openingportions 402H and 4021, the first substrate 306 that is exposed in theopening portions 402D and 402E, and the optical waveguide 308 that isexposed in the opening portions 402F and 402G, to obtain the structure400F. The second dielectric layer 312 is a thin-film dielectricmaterial. Examples of the materials used for forming the seconddielectric layer 312 may include a photosensitive polyimide dielectricmaterial.

With reference to FIG. 4D, the second dielectric layer 312 is thenpatterned by using a third patterned mask (not shown). In an embodiment,the photolithography technique may be used for patterning the seconddielectric layer 312. In the photolithography technique, the seconddielectric layer 312 may be exposed to light by way of the secondpatterned mask. Due to patterning of the second dielectric layer 312,the first substrate 306 is exposed in opening portions 402J and 402K,the optical waveguide 308 is exposed in opening portions 402L and 402M,the first dielectric layer 310 is exposed in opening portions 402N and402O, and the first metal layer 314 is exposed in opening portions402P-402R to obtain the structure 400G. The second metal layer 316 isthen deposited on the second dielectric layer 312 that is exposed inopening portions 402S and 402T to obtain the structure 400H.

With reference to FIG. 4E, the third metal layer 318 is deposited on thefirst metal layer 314 that is exposed in the opening portion 402P toobtain the structure 400I. The second and third metal layers 316 and 318are conductive metal layers. The second metal layer 316 has a lowermelting point than the third metal layer 318. Examples of materials usedfor forming the second metal layer 316 include gold, chromium, aluminum,silver, platinum, nickel, copper, rhodium, palladium, tungsten, andcombinations of such materials. The third metal layer 318 has a eutecticcomposition, such as gold-tin alloy.

The first substrate 306 is then etched at the opening portion 402J toform the v-groove 320 by using self-alignment lithography technique. Thev-groove 320 is formed adjacent to the optical waveguide 308 that isexposed in the opening portion 402L. The structure 400J illustrates thev-groove 320. The position of the v-groove 320 is such that when anoptical fiber is placed in the v-groove 320, an exit facet of theoptical waveguide 308 is accurately aligned to the centre of the opticalfiber. The exit facet of the optical waveguide 308 is adjacent to thev-groove 320.

With reference to FIG. 4F, a fourth metal layer 404 is then formed on abottom surface of the first substrate 306 to obtain the structure 400K.Examples of materials used for forming the fourth metal layer 404include gold, chromium, aluminum, silver, platinum, nickel, copper,rhodium, palladium, tungsten, and combinations of such materials.

The structure 400K illustrates the first sub-mount 302A of thepre-singulated wafer 300 along the section A-A′ axis as shown in FIG. 3. The multilayered structure, including the first dielectric layer 310,the first metal layer 314, the second dielectric layer 312, and thesecond metal layer 316, formed on the optical waveguide 308 is asub-mount boundary wall 406 of the first sub-mount 302A. The third metallayer 318 represents a die-attachment site of the first sub-mount 302A.The height of the sub-mount boundary wall 406 of the first sub-mount302A is same as the heights of the sub-mount boundary walls of the othersub-mounts, such as the second through fourth sub-mounts 302B-302D,thereby enabling a uniformity of topography height across thepre-singulated wafer 300.

Referring now to FIGS. 5A and 5B, steps for fabricating a cap-wafer, inaccordance with an embodiment of the present invention, are shown.

A perspective view 500A illustrates a second substrate 502 on which afifth metal layer 504 is formed. The fifth metal layer 504 is formed byusing the pattern deposition technique. Examples of materials used forforming the fifth metal layer 504 include gold, chromium, aluminum,silver, platinum, nickel, copper, rhodium, palladium, tungsten, andcombinations of such materials. The second substrate 502 is then etchedto form first through fourth depressions 506A-506D on the secondsubstrate 502, as illustrated in a perspective view 500B. The fifthmetal layer 504 prevents the etching of a portion of the secondsubstrate 502 that lies beneath the fifth metal layer 504, therebyresulting in the formation of first through fourth cap boundary walls508A-508D. Each of the first through fourth cap boundary walls 508A-508Dincludes the fifth metal layer 504 and the portion of the secondsubstrate 502 that lies beneath the fifth metal layer 504.

With reference to FIG. 5B, the second substrate 502 is completely etchedat opening portions 510A-510L to obtain the structure illustrated in aperspective view 500C. Due to etching of the second substrate 502 at theopening portions 510A-510L, first through twelfth openings 512A-512L areformed on the second substrate 502.

The structure illustrated in the perspective view 500C is a cap-wafer514 that has first through fourth caps 516A-516D. The first cap 516A hasthe first depression 506A, the first cap boundary wall 508A thatincludes the fifth metal layer 504, and the first through fourthopenings 512A-512D. The second through fourth caps 516B-516D arestructurally and functionally similar to the first cap 516A. In anembodiment, the cap-wafer 514 may be fabricated to match thepre-singulated wafer 300. Further, the height of the first throughfourth cap boundary walls 508A-508D is same across the cap-wafer 514,thereby enabling a uniformity of topography height across the cap-wafer514.

In an embodiment, the cap-wafer 514 may be attached to thepre-singulated wafer 300, such that the fifth metal layer 504 of thecap-wafer 514 is bonded to the second metal layer 316 of thepre-singulated wafer 300. The attachment of the cap-wafer 514 to thepre-singulated wafer 300 is explained in conjunction with FIGS. 7A-7C.

Referring now to FIG. 6 , a cross-sectional view 600 of the first cap516A along section B-B′ of the cap-wafer 514 of FIGS. 5A and 5B, inaccordance with an embodiment of the present invention is shown. Thecross-sectional view 600 illustrates the second substrate 502, the firstdepression 506A, the first cap boundary wall 508A, and the fifth metallayer 504 of the first cap 516A.

Referring now to FIGS. 7A-7C, cross-sectional views 700A-700Cillustrating a wafer-level optoelectronic packaging method, inaccordance with an embodiment of the present invention, are shown. Withreference to FIG. 7A, the cross-sectional view 700A illustrates a firstoptical die 702A that is attached to the first sub-mount 302A. Thecross-sectional view 700A further illustrates second through fourthoptical dies 702B-702D. The first through fourth optical dies 702A-702Dare hereinafter referred to as “optical dies 702A-702D”.

The first optical die 702A includes a bond pad 704A and an opticalcoupler 704B. In an embodiment, the first optical die 702 may furtherhave alignment features (not shown). The alignment features are fiducialmarks that are formed at corners, edges, or center of the first opticaldie 702. Further, the first sub-mount 302A may also include thealignment features (not shown) that correspond to the alignment featuresof the first optical die 702. In one embodiment, the first sub-mount302A may further include one or more micro-machined mating features (notshown), such as stand-offs and stop-blocks. The first optical die 702Ais a single-mode circuitry that is formed by integrating varioussingle-mode photonic devices, such as the optical coupler 704B, an arraywaveguide grating (AWG) (not shown), and a mode-size-converter (notshown). The first optical die 702A emits an optical signal that issingle-mode. The second through fourth optical dies 702B-702D arestructurally and functionally similar to the first optical die 702A.Examples of the first through fourth optical dies 702A-702D may includewaveguide-based diode lasers, photo-detectors, planar lightwave circuits(PLCs), and the like.

For attaching the first optical die 702A to the first sub-mount 302A,the pre-singulated wafer 300 of FIG. 3 is placed on a placement bench(not shown) of a die-placement tool (not shown). The die-placement toolplaces the first optical die 702A on the first sub-mount 302A, such thatthe bond pad 704A of the first optical die 702A comes in contact withthe third metal layer 318. For placing the first optical die 702A on thefirst sub-mount 302A, the die-placement tool aligns the alignmentfeature of the first optical die 702A with the alignment feature of thefirst sub-mount 302A by using optical microscopy alignment method. Inone example, the die-placement tool uses an optical microscope (notshown) to align the alignment feature of the first optical die 702A withthe alignment feature of the first sub-mount 302A, such that thealignment feature of the first optical die 702A overlaps the alignmentfeature of the first sub-mount 302A. In one embodiment, the matingfeatures of the first sub-mount 302A may further aid in an accuratealignment of the first optical die 702A on the first sub-mount 302A.

The die-placement tool further places the remaining optical dies, suchas the second through fourth optical dies 702B-702D, one by one on thesecond through fourth sub-mounts 302B-302D, respectively, by repeatingthe process similar to the process for the placement of the firstoptical die 702A, as explained in the foregoing description. It will beapparent to a person having ordinary skill in the art that more than oneoptical dies may be placed on a single sub-mount without deviating fromthe scope of the invention.

When the first through fourth optical dies 702A-702D are placed on thefirst through fourth sub-mounts 302A-302D, the pre-singulated wafer 300of FIG. 3 is unloaded from the placement bench of the die-placement tooland placed on reflow bench of a reflow station (not shown). In thereflow station, the pre-singulated wafer 300 is reflowed at a firsttemperature ‘T0’, such as 278.degree. C., to permanently attach theoptical dies 702A-702D to the first through fourth sub-mounts 302A-302D,respectively. When the first optical die 702A is attached to the firstsub-mount 302A, the optical waveguide 308 that is adjacent to the firstoptical die 702A is accurately aligned with the optical coupler 704B ofthe first optical die 702A. The pre-singulated wafer 300 having theoptical dies 702A-702D permanently attached to the first through fourthsub-mounts 302A-302D, respectively, is hereinafter referred to as apopulated pre-singulated wafer 706. The populated pre-singulated wafer706 illustrated in the cross-sectional view 700A is along the sectionA-A′ of the pre-singulated wafer 300 of FIG. 3 . A top view of thepopulated pre-singulated wafer 706 is shown in FIG. 8A.

With reference to FIG. 7B, the populated pre-singulated wafer 706 isunloaded from the reflow bench and placed on a placement bench (notshown) of a cap-placement tool (not shown). The cap-placement toolpicks-up and places the cap-wafer 514 of FIG. 5B on the populatedpre-singulated wafer 706. Thus, the first cap 516A overlaps the firstsub-mount 302A. Further, the second metal layer 316 of the firstsub-mount 302A comes in contact with the fifth metal layer 504 of thefirst cap 516A. It will be apparent to a person having ordinary skill inthe art that when the cap-wafer 514 is placed on the populatedpre-singulated wafer 706, the second through fourth caps 516B-516Doverlap the second through fourth sub-mounts 302B-302D.

The first cap 516A, when placed over the first sub-mount 302A, forms acavity 708 for enclosing the first optical die 702A. The cavity 708 is ahermetically sealed cavity for preventing any damage to the firstoptical die 702A from external environment.

Further, the cap-wafer 514 and the populated pre-singulated wafer 706are reflowed at a second temperature “T1” to permanently attach thecap-wafer 514 to the populated pre-singulated wafer 706 for obtaining anencapsulated pre-singulated wafer 710. A top view of the encapsulatedpre-singulated wafer 710 is shown in conjunction with FIG. 8B. Thesecond temperature “T1” is kept lower than the first temperature ‘TO’for preventing a secondary reflow of the third metal layer 318. Theencapsulation of the populated pre-singulated wafer 706 by using thecap-wafer 514 is performed at wafer-level. Since the pre-singulatedwafer 300 and the cap-wafer 514 have uniform topography height, theattachment of the cap-wafer 514 to the pre-singulated wafer 300 isuniform.

In one embodiment, the cap-wafer 514 may be diced to separate the firstthrough fourth caps 516A-516D before being placed on the populatedpre-singulated wafer 706. In such a scenario, the first through fourthcaps 516A-516D are placed on the first through fourth sub-mounts302A-302D, respectively, one after the other, and then the reflowoperation is performed to permanently attach the first through fourthcaps 516A-516D to the first through fourth sub-mounts 302A-302D,respectively, for obtaining the encapsulated pre-singulated wafer 710.

With reference to FIG. 7C, the encapsulated pre-singulated wafer 710 isthen loaded on a placement bench (not shown) of a dicing tool (notshown). The dicing tool singulates the encapsulated pre-singulated wafer710 along the first and second singulation axis 304A and 304B to obtaina first optoelectronic package 712 and second through fourthoptoelectronic packages (as shown in FIG. 8C). The first optoelectronicpackage 712 includes the first optical die 702A enclosed in the cavity708 formed by the first sub-mount 302A and the first cap 516A, and thev-groove 320 that is external to the cavity 708.

An optical fiber 714 is then placed in the v-groove 320 by using theoptical microscopy alignment method. The optical fiber 714, when placedin the v-groove 320, gets automatically aligned to the portion of theoptical waveguide 308 that lies outside the cavity 708. The opticalwaveguide 308 that lies inside the cavity 708 is aligned with the firstoptical die 702A, and the optical waveguide 308 that lies outside thecavity 708 is aligned with the optical fiber 714. Hence, the opticalwaveguide 308 serves as an interconnection conduit between the firstoptical die 702A and the optical fiber 714 for the propagation of anoptical signal (not shown) emitted by the first optical die 702A. Thefirst optical die 702A emits the optical signal that is received by theoptical waveguide 308. The optical signal propagates through the opticalwaveguide 308 which couples the optical signal to the optical fiber 714.The accurate alignment of the optical waveguide 308 with the firstoptical die 702A and the optical fiber 714, achieves a couplingefficiency which is greater than 50%. The first optoelectronic package712 may be mounted on an optical module assembly (not shown) by way ofthe fourth metal layer 404.

The first optoelectronic package 712 manufactured by the method asexplained in the foregoing, has the optical waveguide 308 that isaccurately aligned with the first optical die 702A for receiving theoptical signal from the first optical die 702A, and is further alignedwith the optical fiber 714 for coupling the optical signal to theoptical fiber 714. As the optical waveguide 308 serves as aninterconnection conduit between the first optical die 702A and theoptical fiber 714 for propagating the optical signal emitted by thefirst optical die 702A, the first optoelectronic package 712 henceprevents the propagation of the optical signal in free space, andthereby reduces the propagation losses and increases the couplingefficiency. The optical waveguide 308 further eliminates the need ofadditional components, such as lenses, grating couplers, for couplingthe optical signal from the first optical die 702A to the optical fiber714, and therefore the first optoelectronic package 712 has a largewavelength bandwidth.

Referring now to FIGS. 8A-8C, top views that illustrate the wafer-leveloptoelectronic packaging method, in accordance with an embodiment of thepresent invention, are shown. With reference to FIG. 8A, the top viewillustrates the populated pre-singulated wafer 706 of FIG. 7A. The firstthrough fourth optical dies 702A-702D are permanently attached to thefirst through fourth sub-mounts 302A-302D, respectively.

With reference to FIG. 8B, the top view illustrates the encapsulatedpre-singulated wafer 710 that is formed when the cap-wafer 514 ispermanently attached to the populated pre-singulated wafer 706. Thefirst opening 512A of the first cap 516A exposes the v-groove 320, wherethe optical fiber 714 is placed, and the second and third openings 512Band 512C expose the first metal layer 314 that lies outside the cavity708.

With reference to FIG. 8C, the top view illustrates the firstoptoelectronic package 712 and the second through fourth optoelectronicpackages 802-806 formed by dicing the encapsulated pre-singulated wafer710 along the first and second singulation axis 304A and 304B. Thesecond through fourth optoelectronic packages 802-806 are structurallyand functionally similar to the first optoelectronic package 712 asshown in FIG. 7C.

Referring now to FIG. 9 , a flow chart that illustrates the wafer-leveloptoelectronic packaging method of FIGS. 7A-7C and FIGS. 8A-8C, inaccordance with an embodiment of the present invention is shown.

At step 902, the pre-singulated wafer 300 having a plurality ofsub-mounts, such as the first through fourth sub-mounts 302A-302D, isfabricated by performing the steps as explained in the foregoing. Atstep 904, the first through fourth optical dies 702A-702D are attachedto the first through fourth sub-mounts 302A-302D, respectively, of thepre-singulated wafer 300.

At step 906, it is determined whether all the optical dies, such as thefirst through fourth optical dies 702A-702D are attached to thecorresponding sub-mounts, such as the first through fourth sub-mounts302A-302D, respectively. If at step 906, it is determined that all theoptical dies 702A-702D are not attached to the first through fourthsub-mounts 302A-302D, respectively, step 904 is repeated, and a nextoptical die is attached to the corresponding sub-mount. If at step 906,it is determined that the optical dies 702A-702D are attached to thefirst through fourth sub-mounts 302A-302D, respectively, step 908 isperformed.

At step 908, the cap-wafer 514 including a plurality of caps, such asthe first through fourth caps 516A-516D, is attached to thepre-singulated wafer 300 that has all the optical dies 702A-702Dpermanently attached to the first through fourth sub-mounts 302A-302D,respectively, to obtain the encapsulated pre-singulated wafer 710.

At step 910, the encapsulated pre-singulated wafer 710 is diced toobtain a plurality of optoelectronic packages, such as the first throughfourth optoelectronic packages 712, and 802-806. At step 912, theoptical fiber 714 is placed in the v-groove 320 of the firstoptoelectronic package 712 for receiving the optical signal emitted bythe first optical die 702A by way of the optical waveguide 308. Opticalfibers that are similar to the optical fiber 714 may be placed in thev-grooves of the other optoelectronic packages of the plurality ofoptoelectronic packages.

Thus, each of the first through fourth optoelectronic packages 712 and802-806 manufactured by the method as explained in the foregoing,prevents the propagation of the optical signal in free space, andthereby reduces the propagation losses. The first through fourthoptoelectronic packages 712 and 802-806 further do not requireadditional components, such as lenses, grating couplers, for couplingthe optical signal from the corresponding optical die to thecorresponding optical fiber, and therefore has a large operationalwavelength bandwidth with increased coupling efficiency.

Techniques consistent with the present invention provide, among otherfeatures, methods for wafer-level semiconductor die attachment. Whilevarious exemplary embodiments of the disclosed system and method havebeen described above it should be understood that they have beenpresented for purposes of example only, not limitations. It is notexhaustive and does not limit the invention to the precise formdisclosed.

In the claims, the words ‘comprising’, ‘including’ and ‘having’ do notexclude the presence of other elements or steps then those listed in aclaim. The terms “a” or “an,” as used herein, are defined as one or morethan one. Unless stated otherwise, terms such as “first” and “second”are used to arbitrarily distinguish between the elements such termsdescribe. Thus, these terms are not necessarily intended to indicatetemporal or other prioritization of such elements. The fact that certainmeasures are recited in mutually different claims does not indicate thata combination of these measures cannot be used to advantage.

While various embodiments of the present invention have been illustratedand described, it will be clear that the present invention is notlimited to these embodiments only. Numerous modifications, changes,variations, substitutions, and equivalents will be apparent to thoseskilled in the art, without departing from the spirit and scope of thepresent invention, as described in the claims.

What is claimed is:
 1. A method comprising: forming a layer stack; patterning the layer stack to form a waveguide and a boundary wall, wherein the waveguide and the boundary wall are configured to form an enclosed boundary that encloses an end portion of the waveguide; forming a wiring trace running on top and across the enclosed boundary; attaching at least a device inside the enclosed boundary; and forming a cap, wherein the cap is attached to the enclosed boundary to form a cavity for fully enclosing the at least a device.
 2. The method of claim 1, further comprising: aligning the at least a device with the end portion of the waveguide for receiving an optical signal from the at least a device or for transmitting an optical signal to the at least a device.
 3. The method of claim 1, further comprising: forming an electrical connection coupled to a first portion of the wiring trace for electrically connecting the wiring trace to the at least a device.
 4. The method of claim 1, further comprising: forming a v-groove external to the boundary wall by etching the substrate, wherein the v-groove is configured to support an optical fiber, wherein the optical fiber is configured to be aligned with a second end portion of the waveguide that lies outside the cavity, wherein the optical fiber is configured for receiving the optical signal from the at least a device or for transmitting the optical signal to the at least a device.
 5. The method of claim 1, wherein a top portion of the cap is larger than the surface area of the cavity defined by the boundary wall, wherein the top portion of the cap has a first opening outside of the surface area that exposes a v-groove configured to accept an optical fiber configured to be aligned with the waveguide, wherein the top portion of the cap has a second opening outside of the surface area to expose a portion of the wiring trace that lies outside the cavity.
 6. The method of claim 1, wherein the cap or the enclosed boundary comprises a metal layer, wherein the method further comprises reflowing the metal layer to bond the cap to the enclosed boundary.
 7. A method for wafer-level optoelectronic packaging, the method comprising: providing a first substrate; forming multiple waveguides and multiple boundary walls, wherein a waveguide of the multiple waveguides and a boundary wall of the multiple boundary walls are configured to form an enclosed boundary that encloses a first end portion of the waveguide; attaching one or more devices inside the enclosed boundary; providing a second substrate; patterning the second substrate to form multiple caps with multiple openings outside and between the multiple caps; attaching the second substrate to the first substrate, wherein a cap of the multiple caps is configured to be attached to the enclosed boundary to form a cavity for fully enclosing at least a device of the one or more devices, wherein a first opening of the multiple openings is configured to expose a v groove on the first substrate with the v-groove configured to be coupled to an optical fiber, wherein a second opening of the multiple openings is configured to expose an end of a wiring trace passing through the enclosed boundary.
 8. The method of claim 7, further comprising: aligning the at least device is aligned with the end portion of the waveguide for receiving an optical signal from the at least a device or for transmitting an optical signal to the at least a device.
 9. The method of claim 7, further comprising: forming the wiring trace running on top and across the enclosed boundary, wherein the wiring trace is disposed between two dielectric layers.
 10. The method of claim 7, further comprising: forming the v-groove external to the boundary wall by etching the first substrate, wherein the v-groove is configured to support the optical fiber, wherein the optical fiber is configured to be aligned with a second end portion of the waveguide that lies outside the cavity, wherein the optical fiber is configured for receiving the optical signal from the at least a device or for transmitting the optical signal to the at least a device.
 11. The method of claim 7, wherein at least one of the cap or the enclosed boundary comprises a metal layer, wherein the method further comprises reflowing the metal layer to bond the cap to the enclosed boundary.
 12. The method of claim 7, wherein patterning the second substrate to form the multiple caps comprises forming the first opening outside of a surface area of the cavity defined by the enclosed boundary for placing the optical fiber aligning with a second end portion of the waveguide outside the cavity, and forming the second opening outside of the surface area to expose a portion of the wiring trace outside the cavity, wherein the wiring trace runs on top and across the enclosed boundary.
 13. The method of claim 7, further comprising: dicing the first and second substrates to obtain a plurality of optoelectronic packages, wherein a first optoelectronic package of the plurality of optoelectronic packages comprises the at least a device enclosed within the cavity formed by the cap and the enclosed boundary with the v-groove exposed for coupling to the optical fiber and with the end of the wiring trace exposed.
 14. A method for wafer-level optoelectronic packaging, the method comprising: providing a first substrate; patterning the first substrate to form multiple caps with multiple openings outside and between the multiple caps; attaching the first substrate to a second substrate, wherein a cap of the multiple caps is configured to be attached to an enclosed boundary on the second substrate to form a cavity for fully enclosing at least a device disposed on the second substrate inside the enclosed boundary, wherein a first opening of the multiple openings is configured to expose a v groove on the second substrate with the v-groove configured to be coupled to an optical fiber, wherein a second opening of the multiple openings is configured to expose an end of a metal trace passing through the enclosed boundary.
 15. The method of claim 14, further comprising: aligning the at least a device with the end portion of the waveguide for receiving an optical signal from the at least a device or for transmitting an optical signal to the at least a device.
 16. The method of claim 14, wherein a wiring trace is formed on top and across the enclosed boundary; wherein an electrical connection is coupled to a first portion of the wiring trace for electrically connecting the wiring trace to the at least a device.
 17. The method of claim 14, wherein the v-groove is formed external to the boundary wall, wherein the v-groove is configured to support the optical fiber, wherein the optical fiber is configured to be aligned with a second end portion of the waveguide that lies outside the cavity, wherein the optical fiber is configured for receiving the optical signal from the at least a device or for transmitting the optical signal to the at least a device.
 18. The method of claim 14, wherein at least one of the cap or the enclosed boundary comprises a metal layer, wherein attaching the first substrate to the second substrate comprises reflowing the metal layer to bond the cap to the enclosed boundary.
 19. The method of claim 14, further comprising: dicing the first and second substrates to obtain a plurality of optoelectronic packages, wherein a first optoelectronic package of the plurality of optoelectronic packages comprises the at least a device enclosed within the cavity formed by the cap and the enclosed boundary with the v-groove exposed for coupling to the optical fiber and with the end of the wiring trace exposed.
 20. The method of claim 14, further comprising: coupling the optical fiber in the v-groove of the optoelectronic package after being diced from the first and second substrates, wherein the optical fiber is aligned with a second end portion of the waveguide that lies outside the cavity for receiving an optical signal from the at least a device or for transmitting an optical signal to the at least a device. 